A protection circuit for protecting thin film transistors provided on an active matrix substrate from static electricity has been conventionally proposed. For example, Patent Document 1 indicated below discloses a technique for protecting thin film transistors provided in pixels from static electricity, in a horizontal electric field type liquid crystal display device in which counter electrodes and pixel electrodes are formed on an active matrix substrate. In this liquid crystal display device, common lines are provided that intersect with scanning signal lines and video signal lines outside a display area, and are arranged so as to surround the display area. To portions where the scanning signal lines and the video signal lines intersect with the common lines, non-linear elements are connected. Further, counter voltage signal lines provided outside the display area and connected with the counter electrodes are connected with the common lines via high-resistance elements.
In this liquid crystal display device, even if static electricity enters from the scanning signal lines, the video signal lines, or the common lines, it is diffused via non-linear elements to the common lines, and the thin film transistors of the pixels therefore can be protected from static electricity. Further, since the common lines and the counter voltage signal lines are connected via the high-resistance elements, leakage current via the non-linear elements does not flow through the counter voltage signal lines. With this configuration, the counter voltage is hardly distorted, and the deterioration of the image quality can be decreased.
Further, Patent Document 2 indicated below discloses a configuration of a solid-state image pickup device in which electrostatic protection circuits are connected with the data lines. This electrostatic protection circuit includes a non-linear element connected in a reverse bias state between a data line and a bias line, and a non-linear element connected in a reverse bias state between a data line and a high-potential line to which a potential higher than that of the data line is applied. In this solid-state image pickup device, since the non-linear element connected to the data line, in the electrostatic protection circuit, is in the reverse bias state, leakage current from the data line can be reduced.